\documentclass{ctexart}
\usepackage{avanti}
\everymath{\color{Solarized-magenta}}
\pagestyle{empty} % 没有页眉和页脚

\tikzset{font=\normalsize}

 % define the plot style and the axis style
\tikzset{base/.style={smooth,thick,draw=Solarized-base01}}
\tikzset{arrow/.style={->,>=stealth,base}}
\tikzset{curve/.style={base,Solarized-blue}}
\tikzset{nc/.style={circle, base}}

\begin{document}

\begin{tikzpicture}
    \foreach \i in {1,...,6}
        {
            \node [nc] (x\i) at (2*\i,0) {$x_{\i}$};
        }

    \foreach \i in {1,...,4}
        {
            \node [nc] (a\i) at (2*\i+2,-2) {$a_{\i}$};
        }

    \foreach \i in {1,...,4}
        {
            \pgfmathtruncatemacro{\ip}{\i+1};
            \pgfmathtruncatemacro{\ipp}{\i+2};
            \draw [arrow] (x\i) -- (a\i);
            \draw [arrow] (x\ip) -- (a\i);
            \draw [arrow] (x\ipp) -- (a\i);

            \node at (2*\i+1.2,-1.5) {$w_1$};
            \node at (2*\i+1.75,-1.3) {$w_2$};
            \node at (2*\i+2.4,-1.25) {$w_3$};
        }
\end{tikzpicture}

\end{document}

